This invention relates in general to sound attentuation and, more specifically, to mufflers for use with internal combustion engines or the like.
In many devices such as internal combustion engines, turbine engines, compressed gas powered tools, etc., considerable noise energy travels with exhaust gases. Such noise is objectionable and must often be reduced. A wide variety of mufflers and other noise reducing devices have been developed.
Some mufflers use a plurality of baffles to radically change the path of the exhaust gases over a short distance. While such mufflers may be effective in reducing noise levels, they tend to create undesirably high back pressure on the engine, resulting in lower engine power output and lower efficiency.
Other mufflers direct the exhaust gases straight through a perforated tube within a larger tube, with sound absorbing material such as glass fibers, between the two tubes. These so-called "glass-pack" mufflers produce low back pressure, but are not effective in reducing noise levels.
Attempts have been made to combine baffles and sound absorbing materials to improve muffler efficiency. For example, Cullum in U.S. Pat. No. 2,613,758 uses a combination of concentric tubes with sound absorbing material between a perforated inner tube and an outer tube, a narrow tapered-ended perforated cylinder along the muffler centerline and a set of baffles near the muffler exhaust end. Sanders in U.S. Pat. No. 3,114,431 and Paulsen in U.S. Pat. No. 2,958,388 also disclose mufflers having sound absorbing walls and a core of sound absorbing material within the muffler. While these designs somewhat combine the noise reduction characteristics of the baffle-type muffler and the low back pressure of the straight through type muffler, none provide an optimum combination of high engine efficiency through low back pressure and maximum reduction in noise.
Also, some of these prior mufflers are complex and heavy in construction and others have short useful lives due to corrosion or susceptibility to damage from the hot gases passing through them.
Thus, there is a continuing need for improved mufflers for use with internal combustion engines.